Method of making propargyl chloride



United States Patent METHOD OF MAKING PROPARGYL CHLORIDE Donald H.Wolfe, Lake Jackson, Tex., assignor to The Dow Chemical Company,Midland, Mich, a corporation of Delaware No Drawing. Application August28, 1958 Serial No. 757,675

Claims. (Cl. 260-654) This invention relates to an improved process formaking propargyl chloride, HCEC-CH CI, which is more accurately called3-chloropropyne, and which is used extensively both as an organicreagent and as a constituent of various agricultural fumigantcompositions.

Propargyl chloride has been made in various ways, the commonest being(1) by reaction between propargyl alcohol and thionyl chloride, withpoor yields, and (2) by the gradual introduction of phosgene intopropargyl alcohol and subsequent decomposition of the chloroformic acidpropargyl ester (propargyl chlorocarbonate) in the presence of atertiary amine, also with poor yields, usually of the order of 60-70percent.

It is desired, and it is the principal object of the invention, toprovide an improved method whereby the yield of propargyl chloride maybe consistently of the order 85-95 percent of the theoretical yield.

The improved method of the present invention comprises the gradualintroduction of propargyl alcohol to an excess over the stoichiometricquantity of phosgene in an inert solvent medium, While holding thetemperature at a level not significantly above 5 C., and preferably fromC. to +5 C., then warming slightly to drive oil unreacted and excessphosgene, at a temperature below 40 C., thereupon adding a tertiaryamine as catalyst, and heating to drive off carbon dioxide and to flashdistill the propargyl chloride as it is formed. The success of theprocess, as measured by the improvement in yield, is attributabledirectly to the order of introduction of the reagents, as will be shownhereinafter.

The inert solvent medium for the reaction maybe an aromatic hydrocarbon,preferably one which boils higher than propargyl chloride, suchas'toluene, xylene, cymene, or ethylbenzene, or it may be an aliphatichydrocarbon such as octane, or a mixture of hydrocarbons such asnaphtha, gasoline, or kerosene, or it may be a chlorinated hydrocarbonsuch as ethylene chloride, trichloroethylene, perchloroethylene,chlorobenzene, trichlorobenzene, chloronaphthalene, or a chlorinatedether such as dichloroethylether or chlorinated phenylether. The onlyrequirement is that the medium be a liquid which is inert to phosgene atthe temperatures of exposure and that it be separable from the tertiaryamine employed and from propargyl chloride (when that compound is notemployed as the inert medium). The function of the solvent medium isprimarily to assist in controlling temperature during the reaction,through its diluent effect.

When the reatcion is effected at atmospheric pressure, the temperatureof the solution of phosgene to which the propargyl alcohol is added inthe first step should be kept at or below 5 C. to prevent loss ofphosgene and to prevent Side reactions. Operation at temperatures in therange from -l0 to +5 C. is preferred, as being most convenient, but anylower temperature at which the reaction mixture remains liquid issatisfactory. If desired, the reaction may be elfected at pressuresother than one atmosphere. Thus, reduced. pressures may be used, butthen the reaction temperature must be lowered accordingly to keep thereagents and the solvent from vaporizing. Similarly, superatmosphericpressures may be used, and in such case the reaction temperature may bepermitted to rise somewhat above the preferred range stated above, butthe temperature should neither reach the boiling point of phosgene atthe prevailing pressure nor exceed 40 C., whichever is lower. Because ofthe convenience of operating at atmospheric pressure and the expense ofdoing otherwise, there is little or no reason for employing any otherpressure.

The amount of phosgene employed should be in excess over the amounttheoretically required to react with and esterify the propargyl alcoholto be mixed therewith. Specifically, there should be from 1.05 to 5moles of phosgene for each mole of propargyl alcohol to be added. Asatisfactory and convenient ratio is 1.5 to 1. At early stages of thereaction, of course, the amount of phosgene in the reaction vessel willbe in much greater excess over the amount of propargyl alcohol added upto that time, but this excess will diminish gradually as the reactionproceeds. For this reason, to make the measurements simple, the amountsof reagents to be used are expressed in terms of total moles of phosgeneto be provided for each mole of propargyl alcohol to be added thereto.The phosgene need not all be present before any pro pargyl alcohol isintroduced, but in case only part of the phosgene is present initially,more should be added before the amount of propargyl alcohol introducedexceeds the limiting ratio of one mole of propargyl alcohol for 1.05moles of phosgene.

It is critical to the success of the invention that the propargylalcohol be added to the phosgene rather than adding phosgene to thepropargyl alcohol.

When the esterification reaction is complete, upon completion of theintroduction of propargyl alcohol, the remaining excess phosgene isstripped from the propargyl chlorocarbonate. This is most convenientlydone by Warming the mixture in the reaction vessel to a temperatureabove the boiling point of phosgene (near 8 C. at atmospheric pressure),but temperatures above 40 C. should be avoided at this stage. Other waysof stripping phosgene from the reaction mass are available, including.reduced pressure or vacuum stripping, and stripping by means of bubblinga stream of inert gas (such asnitrogen) through the reaction mass.

When the free phosgene content of the reaction masshas been reduced toan insignificant low level, or to zero, there is added to the remainingliquid a tertiary amine or the salt of such amine. Among the tertiaryamines found useful here are those having the formula wherein R and Rare alkyl (1-6C) or hydroxyalkyl radicals (24C) and R is phenyl, alkyl(1-4C) phenyl, cyclohexyl or one of the values of R or R. Preferred.tertiary amines for the purpose are dimethylaniline, triethylamine andtriethanolamine. The amount of tertiary amine to be employed is notcritical, since this material acts in an apparently catalytic manner, asis known in the art. A convenient, but by no means critical amount oftertiary amine is 5 to 10 percent of the weight of propargylchlorocarbonate theoretically formed in the reaction.

After introduction of the tertiary amine, the mixture is heated to atemperature at which the propargyl chlorocarbonate (or its complex withthe tertiary amine) decomposes with liberation of carbon dioxide toform. propargyl chloride. step is somewhat dependent on the particulartertiary amine employed, but is usually above 40 C. and often ever thedecomposition temperature employed is above The temperature requiredforthis the boiling point of propargyl chloride at the efiectivepressure in the reaction zone, the propargyl chloride vaporizes andleaves the vessel with the conascent carbon dioxide. Insuch case, theefiluent stream of gas and vapors must be cooled to condense thepropargyl chloride so that it may be recovered. If the carbon dioxide isliberated at a temperature below the boiling point (under existingpressure conditions) of propargyl chloride, the latter may be recoveredfrom the liquids left in the reaction zone by any of several methods, ofwhich fractional distillation is one and extraction is another. Forextraction as a recovery means, the liquid in the reactor may be stirredwith water and enough acid to form a water-soluble salt of the tertiaryamine. The water layer may be separated and the propargyl chloride canthen be recovered by fractionaldistillation of the non-aqueous layer.

The first step of the process gives a quantitatively perfect yieldofpropargly chlorocarbonate based on the amount of propargyl alcoholemployed. The second step gives a yield of 85 to 90 percent of thetheoretical amount of propargyl chloride. This yield is increasedslightly in subsequent runs if the tertiary amine from one run is usedagain in the second, because a small part of the propargyl chloridereacts under some conditions with the amine.

The following example illustrates the practice of the invention andshows, by way of comparison, the results obtained by the old procedurehaving a different order of mixing the initial reagents.

Example In accordance with the procedure of this invention, 1,6 moles(160 g.) of phosgene was dissolved in 100 milliliters of xylene. Thesolution was contained in an externally chilled flask fitted with amotor-driven stirrer .and a gooseneck outlet tube connected to ajacketed condenser which could be cooled by water or by iced brine, asdesired. A dropping funnel was mounted so as to discharge into theflask. When the temperature of the phosgene solution had been reduced toabout C., propargyl alcohol was introduced slowly through the droppingfunnel at a rate such as to prevent the heat of reaction from carryingthe temperature above 5 C. In this manner there was added 1 mole (56grams) of propargyl alcohol in the course of 90 minutes. Thereupon thecooling bath was removed and the flask and contents were allowed toattain room temperature. During this time much of the excess phosgeneescaped from the reaction vessel and was condensed and recovered. Theremaining phosgene was driven off by warming the flask and contents to40 C. At this point, analysis of a representative small sample of thereaction mixture showed it to be free of both phosgene and propargylalcohol and to consist of a xylene solution of propargylchlorocarbonate, the yield being 100 percent of theoretical based on thepropargyl alcohol employed. There .was then added to the solution gramsof dimethylaniline and the mixture was heated to a temperature in therange from 95 to 100 C. As the temperature passed 70 0., evolution ofcarbon dioxide and distillation of propargyl chloride were observed. Thehigher temperature maintained both of these results at a practical rateso that, as long as propargyl chlorocarbonate remained in the flask,propargyl chloride was being distilled as a steady stream. When, afterabout 10 to minutes at 95 -100 0., there was no further liquiddistillate being produced, the product was found to be 64.4 grams (0.87mole) of propargyl chloride-an 87 percent yield.

By way of contract (the following old procedure was followed, using thesame apparatus. There was first put into the flask 2.41 moles (135 g.)of propargyl alcohol, dissolved in xylene. This solution was cooled tonear 0 C. There was then introduced slowly 2.52 moles (250 g.) ofphosgene dissolved in cold xylene, at a rate such that the reactiontemperature was controlled in the range from -5 to +5 C. The phosgenewas all added in about 30 minutes. There was then added dimethylanilineto serve as catalyst, and the mixture was heated as in the priorexperiment, to drive off carbon dioxide and propargyl chloride and tocollect the latter. The temperature during this operation, as before,was held near 95-100 C. The propargyl chloride produced weighed 84.5 g.(1.13 moles), and represented a yield of 47 percent of the theoreticalamount. The apparent disadvantage of the procedure just described may bedue to the probability that, when phosgene is added to a momentaryexcess of propargyl alcohol, two competing reactions are possible. Oneof these produces the desired mono propargyl chlorocarbonate and theother produces dipropargyl carbonate. The last named compound cannotform propargyl chloride by simple decarbonation, as can thechlorocarbonate. To the extent, then, that phosgene is permitted to formthe dipropargyl carbonate, the ultimate yield of propargyl chloride isdiminished.

In other procedures of the prior art, yields of propargyl chloride up toabout 70 percent have been reported, but these have involved proceduresin which much of the initial charge of propargyl alcohol was unreacted,and the added recovery step, coupled with low yield, has made themunattractive. To illustrate, the teachings of German Patent No. 821,207show that in the process there disclosed, less than 5 8 percent of theinitial alcohol charge was reacted, and of this, only percent went tothe desired propargyl chlorocarbonate. While there was a yield ofpropargyl chloride near 70 percent, based on unrecovered alcohol, theefiiciency of the process was of the order of 42 percent.

I claim:

1. In the preparation of propargyl chloride from propargyl alcohol andphosgene, the improvement which consists in adding the propargyl alcoholto a solution of phosgene in an inert liquid medium while the solutionof phosgene is at a temperature below 40 C. and below the boiling pointof phosgene at the pressure prevailing in the reaction Vessel, at a ratesuch as to maintain the temperature below both of said limiting values,and discontinuing the introduction of propargyl alcohol before theamount thereof introduced into the reaction vessel exceeds a ratio of 1mole of propargyl alcohol for each 1.05 moles of phosgene theretoforesupplied to said vessel.

2. The improvement claimed in claim 1, wherein the reaction is efiectedat atmospheric pressure and at a temperature not in excess of 5 C. atwhich the reaction mixture is liquid.

3. The improvement claimed in claim 2, wherein the inert liquid mediumis xylene.

4. The method which comprises the improvement claimed in claim 1,wherein after termination of the introduction of propargyl alcohol, theunreacted phosgene is stripped from the reaction mixture, a tertiaryamine is added to the resulting solution of propargyl chlorocarbonate,and the amine-containing solution is heated to a temperature at whichthe said chlorocarbonate liberates carbon dioxide and the propargylchloride so produced is distilled as formed.

5. The method claimed in claim 4, wherein the aminecontaining solutionis heated to a temperature near to C. at atmospheric pressure to eifectrelease of carbon dioxide and flash distillation of propargyl chloride.

References Cited in the file of this patent UNITED STATES PATENTS2,274,611 Hurd Feb. 24, 1942 FOREIGN PATENTS 821,207 Germany Nov. 15,1951

1. IN THE PREPARATION OF PROPARGYL CHLORIDE FROM PROPARGYL ALCOHOL ANDPHOSGENE, THE IMPROVEMENT WHICH CONSISTS IN ADDING THE PROPARGYL ALCOHOLTO A SOLUTION OF PHOSGENE AND IN AN INERT LIQUID MEDIUM WHILE THESOLUTION OF PHOSGENE IS AT A TEMPERATURE BELOW 40*C. AND BELOW THEBOILING POINT OF PHOSGENE AT THE PRESSURE PREVAILING IN THE REACTIONVESSEL, AT A RATE SUCH AS TO MAINTAIN THE TEMPERATURE BELOW BOTH OF SAIDLIMITING VALUES, AND DISCONTINUING THE INTRODUCTION OF PROPARGYL ALCOHOLBEFORE THE AMOUNT THEREOF INTRODUCED INTO THE REACTION VESSEL EXCEEDS ARATIO OF 1 MOLE OF PROPARGYL ALCOHOL FOR EACH 1.05 MOLES OF PHOSGENETHERETOFORE SUPPLIED TO SAID VESSEL.